using the relay for my two channel build

[Curranm]

I have a two channel "london" preamp built and working wonderfully on a set of KT88's I want to make is footswitchable, I have the hoffman board's build and ready to install BUT I do not know how to integrate this into my amp. would I remove the switch I have in the amp and connect the wires from this set up TO the relay? and then a spst would be panel mounted to facilitate for manual switching with no foot switch? and if so LOOKING at the schematic of the switching I think I would take the bottom leads of the switch for the drive channel and attach them to the always closed (pin6/11) on the relay. then the clean channel connection would be on (pin 8 or 9) with the ground connection going to (pin4/13) am I correct?

[PRR]

Welcome.

I think you got it.

[Curranm]

well BOOOO the rectifier started to smoke.

[Curranm]

so I have double checked things here and I cna see NO reason for the rectifier to start smoking. before I wired in the relay, jack, and switch I was getting my 5v off of the lug referenced against the ground lug on the board. I now have the power board grounded to the switch and into the jack. I am showing continuity and the ground from the power board never lifts or goes away. what have I missed here?

[sluckey]

Your rectifier is dead now. Gonna need a new one or use 4 individual diodes. I'm guessing you are connecting the power supply board to the filament string. And you have a filament winding center tap connected to chassis. If so...

          ***CAUTION***
DO NOT CONNECT ANY PART OF THAT POWER SUPPLY BOARD TO CHASSIS GROUND!

[Curranm]

yes I am using the AC heaters to power the board and yes I am running the ground to the chassis............. the heaters are CT grounded to the chassis. so how is this grounded then? everything else in the relay that goes to ground should BUT the power board should NOT be grounded at all?

[Curranm]

I have this guy laying around which I bought a few weeks ago

http://www.mouser.com/ProductDetail/Rectron/BR305/?qs=%2fha2pyFadugRZ13zZfhn%252bEkPrrS%2fOclstbHjV5pKmzU%3d

[sluckey]

That Mouser bridge is perfect. But if you don't disconnect that power supply board "grnd" turret from chassis, you will smoke the new bridge as soon as you flip the power switch. This also means you cannot use a footswitch jack that connects to the chassis. Use an isolated jack such as a Cliff style, or get a couple insulating shoulder washers for a Switchcraft style jack.

Since your PT filament winding has a center tap connected to chassis you must float the ground for the +5V supply. This little supply board does not need to share the chassis ground with the rest of the amp.

[Curranm]

I can use the isolaters that come with the cliff jacks right? I hat cliff jacks BUT I can use those with the switch craft and that will "FLOAT" the ground away from the chassis ground yes? it will all be it own little ground circuit

[sluckey]

I don't think the cliff washers will work with the Switchcraft jacks. If you have a Cliff jack, just use that. If you must use a Switchcraft jack, then use the correct bushing washers. You'll need two. And if your chassis is very thick you'll also need to get the long bushing Switchcraft L12A jack. You'll also need to drill a 1/2" hole in the chassis.

However you isolate the jack be sure the power supply ground is floated from the chassis. Just use your ohm meter and measure resistance between chassis and the "grnd" turret on the power supply board. Resistance should be very high , ideally infinity ohms.

[Curranm]

pic's of the relay re-wiring BEFORE I fire her up again!!!! this is the cliff jack, and the dpst switch. there is a constant ground to the power board with the switch engaged or not. when the switch is open there is ONLY ground going to the ground lug of the cliff jack from the power board through the switch. with it closed the ground goes through the power board, the cliff ground and the two tips of the cliff jack.

[Curranm]

here is the relay wiring, the yellow wire going into the diode is coming off of the 5v from the power board. the white wire is coming from the tip of the cliff jack going to the other side of the diode on the relay. it shows continuity in ONLY one position on the panel switch.

[Curranm]

pix of the power board. the black wire is the ground coming off of the panel switch. it IS NOT grounded to the chassis.it is only grounded to the cliff jack.

[sluckey]

pix of the power board. the black wire is the ground coming off of the panel switch. it IS NOT grounded to the chassis.it is only grounded to the cliff jack.

I think you have properly floated the relay power supply ground.

But, just to be sure... Before you connect that black wire to the "grnd" turret on the PS board, check for resistance one more time. Connect one meter probe to the dangling black wire. Connect the other meter probe to chassis. You should have infinite ohms reading. Flip your front panel switch back and forth. Meter should read infinite ohms in both positions. Now connect your footswitch or just short between the lugs on the cliff jack. Meter should read infinite ohms for all cases. Meter should never read zero or low ohms for any of the conditions in this paragraph.

One more quick resistance check... Leave one meter probe connected to the dangling black wire at the PS board. Connect the other meter probe to the white wire at the relay board. You should read infinity ohms or zero ohms, depending on the position of the front panel switch. Flip the switch and the meter reading should change.

If both these checks are good you are ready to connect the dangling black wire to the "grnd" turret on the PS board. Now power up, hopefully with no smoke. You should be able to hear the relay click when you flip the front panel switch. If you can't hear it, put the tip of a screwdriver blade on the plastic body of the relay and hold the screwdriver handle firmly against your ear. Should be able to hear it now when you flip the switch.

[tubenit]

We have some excellent information in ARCHIVES on relay switching:

http://el34world.com/Forum/index.php?topic=14348.0

Note reply #25 and #32 on the thread where Sluckey addressed the issue of "ground" with relay supply. 

With respect, Tubenit

[Curranm]

she works great!!!! the switching is super duper! NO I need to find out why one KT88 started to go all bright blue all of a sudden?! blue a fuse and found out that the 100PT from classic tone should probably have a 4A on it even for a 50 watt JTM OT with KT88's. didn't have any of those so I use a 5A like in my laney AOR.